Musical sound generation device, storage medium, and musical sound generation method

ABSTRACT

An address for reading, from a waveform memory connected by a bus, waveform data to be assigned to each of a plurality of sound generation channels for generating a musical sound, is calculated, by time division, for each sound generation channel, and the calculated address and the sound generation channels are associated and stored in an address memory. When the bus is in an empty state, an address stored in the address memory is read, and waveform data is read from the waveform memory based on the read address; the read waveform data is assigned to the corresponding sound generation channel, and generation of a musical sound is prescribed for the sound generation channel to which the waveform data is assigned.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2012-52616, filed Mar. 9,2012, and the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a musical sound generation device forgenerating musical sound by reading waveform data, a storage medium, anda musical sound generation method.

2. Related Art

A musical sound generation device is conventionally known that storessampled waveform data and reads the data to generate musical sound of avariety of frequencies.

For example, Japanese Unexamined Patent Publication No. 2003-157082describes technology in which data of a sound source encoded by PCM(Pulse Coded Modulation) is read by time division, into respective timeslots of respective channels in one sample cycle, to synthesize musicalsounds of a plurality of channels.

In technology described in Japanese Unexamined Patent Publication No.2003-157082, a process is repeated in which waveform data is read frommemory, in time slots of respective channels, and musical sound issynthesized and outputted.

However, conventional musical sound generation devices, including thetechnology described in Japanese Unexamined Patent Publication No.2003-157082, may be configured to have a shared memory in which thememory storing the waveform data is shared with another application, dueto cost reduction demands.

In a case in which the memory storing the waveform data is shared, theremay be an increase in the probability of collisions with regard toaccess to memory by plural processes, resulting in access to memorybeing made to wait, and leading to delays in processing.

In particular, in a case of an increase in the number of musicalchannels that can be simultaneously generated, this type of situationbecomes conspicuous.

In this way, in a conventional musical sound generation device,processing efficiency for generating musical sound has not beensufficiently high.

SUMMARY OF THE INVENTION

The present invention has been realized in consideration of this type ofsituation, and has as an object the raising of processing efficiency forgenerating musical sound in a musical sound generation device.

In order to achieve the abovementioned object, a musical soundgeneration device according to an aspect of the present inventionincludes: a plurality of sound generation channels that generate musicalsound; an address calculator that calculates an address in order toread, from a waveform memory connected by a bus, waveform data to beassigned to the respective sound generation channels, by time divisionfor each of the sound generation channels; an address memory thatassociates and stores addresses calculated by the address calculator andthe sound generation channels; a waveform data reader that reads anaddress stored in the address memory, when the bus is in an empty state,and reads waveform data from the waveform memory based on the readaddress; and a waveform generation prescription unit that prescribesassigning waveform data read by the waveform data reader to acorresponding sound generation channel, and generating a musical soundfor the sound generation channel to which said waveform data isassigned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of hardware of anelectronic musical instrument provided with a musical sound generationdevice according to an embodiment of the present invention;

FIG. 2 is a block diagram showing a configuration of the musical soundgeneration device;

FIG. 3 is a block diagram showing a specific configuration of a waveformgeneration unit;

FIG. 4 is a schematic diagram showing a format of a sound source controlparameter;

FIG. 5 is a block diagram showing a specific configuration of a waveformmemory interface unit;

FIG. 6 is a block diagram showing a configuration example of a bustraffic monitoring unit;

FIG. 7 is a schematic diagram showing a format of entry data;

FIG. 8 is a schematic diagram showing a format of request statusinformation;

FIG. 9 is a schematic diagram showing a format of storage areas in asample data buffer RAM;

FIG. 10 is a schematic diagram showing relationships of master counterand time slots of respective channels;

FIG. 11 is a schematic diagram showing a generation procedure of amusical sound generation device in an electronic musical instrument;

FIG. 12 is a schematic diagram showing states in which entry data isstored in RAM;

FIG. 13 is a flowchart showing entry data generation processing; and

FIG. 14 is a flowchart showing waveform generation processing.

DETAILED DESCRIPTION OF THE INVENTION

A description is given below of embodiments of the present invention,using the drawings.

First Embodiment

Overall Configuration

FIG. 1 is a block diagram showing a configuration of hardware of anelectronic musical instrument provided with a musical sound generationdevice according to an embodiment of the present invention.

The musical sound generation device 20 is configured, for example, as asound source of the electronic musical instrument 1. It is to be notedthat in the present embodiment a description is given citing a case inwhich the electronic musical instrument 1 is realized as a keyboardinstrument such as an electronic piano or the like, but configurationswith other musical instruments are also possible.

In FIG. 1, the electronic musical instrument 1 is provided with a memory12 formed of a CPU (Central Processing Unit) 11, a ROM (Read OnlyMemory), a RAM (Random Access Memory) or the like, a memory controller13, a bus 14, an input unit 15, the musical sound generation device 20,and a mixer 21.

The CPU 11 executes various types of process in accordance with aprogram recorded in the ROM, which is inside the memory 12. For example,the CPU 11 executes a process of generating, in the musical soundgeneration device 20, sound corresponding to a key-pressing actioninputted via the input unit 15 formed of a keyboard, or executes aprocess related to a setting of the electronic musical instrument 1inputted by a user.

Furthermore, with regard to the CPU 11 or the musical sound generationdevice 20 executing various types of process, necessary data and thelike are stored as appropriate in the RAM within the memory 12. That is,the RAM forms shared memory that is shared by respective functionalparts in the overall electronic musical instrument 1. Specifically,parameters and the like, used when the various types of process forscreen display are executed by the CPU 11, are stored in the RAM.

The memory controller 13 controls access to memory by the CPU 11 or themusical sound generation device 20. Specifically, the memory controller13 operates as a bus slave with regard to the CPU 11 that operates as abus master or the musical sound generation device 20, and reads datafrom a prescribed address in response to a request from the bus master.

The CPU 11 and the memory 12 are connected to one another via a bus 14.Furthermore, the input unit 15 and the musical sound generation device20 are also connected to the bus 14.

An input unit 15 is provided with the keyboard and a switch forinputting various types of information. The input unit 15, in a casewhere a key is pressed, outputs a key number for identifying the key,and information (referred to below as “velocity”) indicating theintensity with which the key was pressed, to the CPU 11, and outputsvarious types of information inputted by the user to the CPU 11.

Besides these, the electronic musical instrument 1 may have a display ora speaker and DAC, or the like, for outputting an image or voice.Moreover, a hard disk or DRAM (Dynamic Random Access Memory) for storingvarious types of program and data for controlling the electronic musicalinstrument 1 may be added.

The musical sound generation device 20 reads waveform data stored in thememory 12, in response to an instruction of the CPU 11, and generates amusical sound (specifically, a digital signal expressing a musicalsound). In the present embodiment, a description is given in which themusical sound generation device 20 has a polyphonic function that cansimultaneously generate sound in 128 channels, and executes processingto generate sounds in each channel ch0 to ch127, for each one cycle(time slot) obtained by dividing one sample cycle into 128 parts. It isto be noted that a specific configuration of the musical soundgeneration device 20 will be described later.

The mixer 21 synthesizes a musical sound generated by the musical soundgeneration device 20, and outputs to a DAC or the like, not shown in thedrawings. The DAC converts a digital signal representing a musical soundinputted from the mixer 21 to an analog signal, and outputs to a speakeror the like.

Configuration of the Musical Sound Generation Device 20

Next, a description is given concerning a configuration of the musicalsound generation device 20.

FIG. 2 is a block diagram showing the configuration of the musical soundgeneration device 20.

In FIG. 2, the musical sound generation device 20 is provided with awaveform generation unit 100 and a waveform memory interface unit 200.Both the waveform generation unit 100 and the waveform memory interfaceunit 200 are connected to a bus 14, and the waveform generation unit 100supplies an entry request, entry data, and an address to the waveformmemory interface unit 200, and conversely receives data from thewaveform memory interface unit 200.

Configuration of the Waveform Generation Unit 100

FIG. 3 is a block diagram showing a specific configuration of thewaveform generation unit 100.

The waveform generation unit 100 operates in accordance with a mastercounter mc generated based on a system clock of the musical soundgeneration device 20. Specifically, 128 time slots for the respectivechannels ch0 to ch127 are prescribed by upper 7 bits of the mastercounter mc configured as a counter of 11 bits. Respective time slots forlower 4 bits of the master counter mc are further divided into 16fields.

With the start of time slots of the respective channels ch0 to ch127, inaccordance with the master counter mc sequentially inputted, as atrigger, the waveform generation unit 100 calculates an address of thememory 12 corresponding to each channel, and outputs to the waveformmemory interface unit 200 with entry information of the channels.

Then, until finish timing of the timeslot of the channel in questionwith regard to a subsequent sampling cycle, a digital signalrepresenting a musical sound is generated using the waveform datainputted from the waveform memory interface unit 200, and is outputtedto the mixer 21.

In FIG. 3, the waveform generation unit 100 is provided with: a soundsource control parameter RAM 101, a mode register 102, address registers103 to 105, a pitch register 106, selectors 107 to 109, a subtractor110, a step value register 111, an adder 112, an entry data generationunit 113, a read address computation circuit 114, a previous-time stepvalue register 115, a waveform computation unit 116, and a RAMarbitration unit 117. It is to be noted that a selection signal showingwhich input signal is selected is inputted from the CPU (not shown inthe drawing), in accordance with processing content of the waveformgeneration unit 100, to the selectors 107 to 109, and data used in astage of each process is delivered to a process of a subsequent stage.

The RAM arbitration unit 117 performs control with regard to access bythe CPU 11 to each of the registers described above via the bus 14, andto selection of operation of the selectors described above.

A storage area corresponding to the respective channels ch0 to ch127 isformed in the sound source control parameter RAM 101, and variousparameters (referred to below as “sound source control parameters”) thatcontrol sound sources are stored in each of the storage areas.

FIG. 4 is a schematic diagram showing a format of a sound source controlparameter stored in the sound source control parameter RAM 101.

In FIG. 4, storage areas corresponding to the channels ch0 to ch127 areformed in the sound source control parameter RAM 101, and a waveformaddress integer part A, a waveform address decimal part a, an addressstep value n, a replay mode value m, a replay pitch data integer part P,a replay pitch data decimal part p, and a wave peak value W are storedin the storage areas of the respective channels. It is to be noted thatthe addresses shown in FIG. 4 schematically represent respective storageareas.

The waveform address integer part A represents an integer part in a readaddress of the memory 12, and the waveform address decimal part arepresents a decimal part in a read address of the memory 12.

The address step value n represents a step value from a current readaddress in the memory 12.

The replay mode value m represents a replay mode indicating whethermusical sound is replayed based on PCM, or is replayed based ondifferential PCM.

The replay pitch data integer part P represents an integer part in pitchwidth accompanying pitch when waveform sample data is read, and thereplay pitch data decimal part p represents an integer part in pitchwidth.

The wave peak value W represents a wave peak value of sample data readfrom the memory 12 in the previous sampling cycle.

Returning to FIG. 3, the mode register 102 temporarily stores the replaymode value m read from the sound source control parameter RAM 101 viathe RAM arbitration unit 117, and the stored replay mode value m isoutputted to the entry data generation unit 113.

The address register 103 temporarily stores the waveform address integerpart A of an address (a next read address in the memory 12) calculatedby the adder 112, and outputs the stored waveform address integer part Ato the selector 109, the subtractor 110 and the entry data generationunit 113.

The address register 104 temporarily stores the waveform address integerpart A read from the sound source control parameter RAM 101 via the RAMarbitration unit 117, and outputs the stored waveform address integerpart A to the selector 108, the subtractor 110, the entry datageneration unit 113, and the read address computation circuit 114.

The address register 105 temporarily stores the waveform address decimalpart a inputted from the selector 107, and outputs the stored waveformaddress decimal part a to the selectors 108 and 109, and a waveforminterpolation processing unit 116 a.

The pitch register 106 temporarily stores a replay pitch data integerpart P and a replay pitch data decimal part p read from the sound sourcecontrol parameter RAM 101 via the RAM arbitration unit 117, and outputsthe stored replay pitch data integer part P and replay pitch datadecimal part p to the adder 112.

The selector 107 selects either of the waveform address decimal part aof the address (a next read address in the memory 12) calculated by theadder 112, or the waveform address decimal part a read from the soundsource control parameter RAM 101, and outputs to the address register105.

The selector 108 selects either of the waveform address integer part Ainputted from the address register 104, or the waveform address decimalpart a inputted from the address register 105, and outputs to the adder112.

The selector 109 selects any of the waveform address integer part Ainputted from the address register 103, the address step value ninputted from the step value register 111, the waveform address decimalpart a inputted from the address register 105, and the wave peak value Winputted from the waveform computation unit 116, and outputs to thesound source control parameter RAM 101 via the RAM arbitration unit 117.

The subtractor 110 subtracts the waveform address integer part A in thecurrent read address inputted by the address register 104, from thewaveform address integer part A in the next read address inputted by theaddress register 103, and computes the address step value n. Thesubtractor 110 then outputs the computed address step value n to thestep value register 111.

The step value register 111 temporarily stores the address step value ninputted from the subtractor 110, and outputs the stored address stepvalue n to the entry data generation unit 113.

The adder 112 adds the waveform address integer part A or the waveformaddress decimal part a inputted from the selector 108, and the replaypitch data integer part P or the replay pitch data decimal part pinputted from the pitch register 106. The adder 112 then outputs theaddition result to the address register 103 or the selector 107. It isto be noted that, in a case where rounding up to an integer occurs byaddition of the waveform address decimal part a and replay pitch datadecimal part p, the adder 112 generates a carry signal, and the roundingup is reflected in the addition result of the waveform address integerpart A and the replay pitch data integer part P.

The entry data generation unit 113 operates by way of a count upwards ofthe master counter mc, and generates information (referred to below as“entry data”) for reading data of a musical sound next generated, fromthe memory 12, in accordance with the replay mode value m inputted fromthe mode register 102. The entry data is a collection of parameters forreading the data of the musical sound generated in a next samplingcycle, from the memory 12.

Specifically, the master counter mc, the replay mode value m from themode register 102, the address step value n from the step value register111, the waveform address integer part A from the address register 103,and the waveform address integer part A from the address register 104are inputted to the entry data generation unit 113. In a case where itis expressed that the inputted replay mode value m is replayed based onPCM, the entry data generation unit 113 sets the waveform addressinteger part A inputted from the address register 103 to the readaddress (referred to below as “request address”) of the memory 12. Onthe other hand, in a case where it is expressed that the inputted replaymode value m is replayed based on differential PCM, the entry datageneration unit 113 sets a result of adding the waveform address integerpart A inputted from the address register 104 and the address step valuen, to the read address (referred to below as “request address”) of thememory 12

Then, with the set request address, the number of words (referred tobelow as “number of request words”) representing read data size, achannel number (any of ch0 to ch127), start flag f representing whetheror not sound generation has started, and the replay mode value m, asentry data, the entry data generation unit 113 outputs to a waveformmemory interface unit 200. At this time, with an entry request signalrepresenting outputting entry data to the waveform memory interface unit200 in a valid state (for example, high level), the entry datageneration unit 113 outputs the entry data.

It is to be noted that in a case of a representation that the inputtedreplay mode value m replays based on PCM, the number of request wordsrepresenting one sample amount in sample data of the waveform isspecified, based on a read address. On the other hand, in a case of arepresentation that the inputted replay mode value m replays based ondifferential PCM, the number of request words representing a sampleamount corresponding to the number of steps, is specified, based on aread address. That is, with differential PCM, since only the differencefrom a preceding sample is shown, as waveform sample data, in a casewhere the number of steps is 2 or more, in order to accumulate sampledata from the current address up to the read address, a word numberrequest to read this is specified.

Here, along with a time slot start for each channel, in synchronizationwith the master counter mc, the entry data generation unit 113 outputsthe entry data of the channel in question to the waveform memoryinterface unit 200. Since output of the entry data does not accompanyaccess to the memory 12, the waveform sample data is read and output isfinished early, in comparison to a case of continuing until a process ofgenerating a musical sound.

There is then no constraint on time slots for each channel, andthereafter waveform sample data read from the memory 12 by the waveformmemory interface unit 200 is used until a time slot finish of thechannel in question in the next sampling cycle, and a musical sound isgenerated by the waveform computation unit 116.

The read address computation circuit 114 computes a read address of asample data buffer RAM 250 for the waveform memory interface unit 200,in accordance with the master counter mc that is sequentially inputted,and outputs to the sample data buffer RAM 250. Specifically, the mastercounter mc, the replay mode value m, the waveform address integer part Astored by the address register 103, and the waveform address integerpart A stored by the address register 104, are inputted to the readaddress computation circuit 114. Then, based on the waveform addressinteger part A stored by the address register 103 or the waveformaddress integer part A stored by the address register 104, the readaddress computation circuit 114 generates an address of the sample databuffer RAM 250 corresponding to the replay mode value m, for each of thechannels ch0 to ch127. The read address computation circuit 114 outputsthe address of the sample data buffer RAM 250 that has been generated,to the sample data buffer RAM 250, for each of the channels ch0 toch127, in synchronization with the master counter mc.

The previous step value register 115 temporarily stores the address stepvalue n read from the sound source control parameter RAM 101 via the RAMarbitration unit 117, and outputs the stored address step value n to thewaveform computation unit 116. The address step value n stored by theprevious step value register 115 is an address step value computed forthe previous sampling cycle, with respect to each channel.

The waveform computation unit 116 generates a digital signalrepresenting a replayed musical sound, from waveform sample data readfrom the sample data buffer RAM 250 of the waveform memory interfaceunit 200, and outputs the generated digital signal to the mixer 21.Specifically, the waveform address decimal part a and the waveformsample data read from the sample data buffer RAM 250 are inputted to thewaveform computation unit 116. The waveform computation unit 116 thenrefers to the waveform sample data read from the sample data buffer RAM250 and computes the wave peak value W.

Furthermore, the waveform computation unit 116 is provided with awaveform interpolation processing unit 116 a that uses the waveformaddress decimal part a to perform interpolation processing (for example,liner interpolation or the like) among the waveform sample data. In acase in which an address between the sample data is specified, thewaveform computation unit 116 computes the wave peak value W byperforming waveform interpolation processing by the waveforminterpolation processing unit 116 a. That is, a digital signalindicating a musical sound is generated by the waveform computation unit116. The waveform computation unit 116 then outputs the computed wavepeak value W to the selector 109. Furthermore, the waveform computationunit 116 outputs the generated digital signal to the mixer 21.

Configuration of Waveform Memory Interface Unit 200

When entry data is inputted from the waveform generation unit 100, thewaveform memory interface unit 200 temporarily stores the inputted entrydata, and reads waveform sample data corresponding to the stored entrydata from the memory 12, at timing at which the bus 14 is in an emptystate.

The waveform memory interface unit 200 then temporarily stores the readwaveform sample data, and outputs the stored waveform sample data, inresponse to a read request (input of an address by the read addresscomputation circuit 114) from the waveform generation unit 100, to thewaveform generation unit 100.

FIG. 5 is a block diagram showing a specific configuration of thewaveform memory interface unit 200.

In FIG. 5, the waveform memory interface unit 200 is provided with anentry processing unit 210, an entry RAM 220, a request status RAM 230, amemory bus interface unit 240, a and sample data buffer RAM 250.

When the entry data is inputted from the waveform generation unit 100,the entry processing unit 210 stores the entry data in an area formedfor each sound generation channel in the entry RAM 220. Furthermore, onreading waveform sample data from the memory 12 in accordance with theentry data, the entry processing unit 210 generates request statusinformation (described later) representing content of the previous readrequest, based on a reading result. The entry processing unit 210 thenstores the request status information in an area formed for each channelin the request status RAM 230.

Furthermore, the entry processing unit 210 generates specificinformation (referred to below as “memory request information”, asappropriate) for reading waveform sample data from the memory 12, basedon the request status information and the entry data. The entryprocessing unit 210 reads the waveform sample data from the memory 12via the bus 14, in accordance with the memory request information.

Moreover, the entry processing unit 210 refers to a monitoring signalfrom a bus traffic monitoring unit 217 provided in each part,functioning as a bus master, and determines the data amount read at atime from the memory 12. That is, in a case where empty bus time perunit of time is longer, the entry processing unit 210 sets the dataamount read at a time from the memory 12 to be larger, and in a casewhere the empty bus time per of unit time is shorter, sets the dataamount read at a time from the memory 12 to be smaller.

As shown in FIG. 5, the entry processing unit 210 is provided with anentry data control unit 211, a write pointer register 212, anincrementer 212 a, a read pointer register 213, an incrementer 213 a, abus arbitration unit 214, an entry data register 215, a status dataregister 216, a bus traffic monitoring unit 217, and a memory requestcontrol unit 218.

On receiving an entry request signal from the waveform generation unit100, the entry data control unit 211 inputs a latch signal to the writepointer register 212, and increments by 1 an address indicated by thewrite pointer.

Furthermore, entry data from the entry data register 215 and requeststatus information from the status data register 216 are inputted to theentry data control unit 211. The entry data control unit 211 thengenerates the memory request information based on the entry data and therequest status information. For example, the entry data control unit 211refers to an address and number of words shown in the entry data, andthe an address and number of words that have been read, as shown in therequest status information, and generates memory request information soas to read data subsequent to data that has already been read. The entrydata control unit 211 then outputs the generated memory requestinformation to the memory request control unit 218.

Here, the entry data control unit 211 refers to traffic information fromthe bus traffic monitoring unit 217 and a bus traffic monitoring unitprovided in another bus master, and while dynamically determining thedata amount read at a time from the memory 12, a read data amount thathas been determined is included in the memory request information. As aresult, an operation in which the waveform sample data are read to thewaveform memory interface unit 200 from the memory 12 is performedefficiently in accordance with an empty state of the bus 14.

Furthermore, when the reading of the waveform sample data shown in thememory request information from the memory 12 is complete, a signalindicating reception completion is inputted to the entry data controlunit 211 from the memory request control unit 218. In a case wherepreparation for a subsequent reading from the memory 12 is completed,the entry data control unit 211 outputs new memory request informationto the memory request control unit 218, and data reading continues.

Furthermore, when reading of the waveform sample data of each channelvia the memory request control unit 218 is performed, the entry datacontrol unit 211 outputs a write enable signal together with an addressof the request status RAM 230 corresponding to a result of the reading(an address specifying a storage area of each channel) and write data(that is request status information) to the request status RAM 230.Furthermore, in a case of reading entry data from the entry RAM 220, theentry data control unit 211 outputs an address indicating a storage areaof the same channel to the request status RAM 230, and stores therequest status information from the address in question in the readstatus data register 216.

The write pointer register 212 stores a write pointer indicating a writeaddress of the entry data in the entry RAM 220. The write pointer valueis incremented by 1 by the incrementer 212 a, in response to a latchsignal outputted from the entry data control unit 211 each time an entryrequest signal is inputted, and returns to 0 when a maximum value isreached. In this way, each area of the entry RAM 220 is cyclicallyspecified.

The read pointer register 213 stores a read pointer indicating a readaddress of the entry data in the entry RAM 220. The read pointer valueis incremented by 1 by the incrementer 213 a, with the read requestsignal as a latch signal, each time the entry data is read from theentry RAM 220 by the entry data control unit 211, and returns to 0 whena maximum value is reached. In this way, each area of the entry RAM 220is cyclically specified.

The bus arbitration unit 214 arbitrates specification of a write addressfrom the write pointer register 212 and specification of a read addressfrom the read pointer register 213. As a result of the arbitration, in acase of receiving a specification of the write address from the writepointer register 212, the bus arbitration unit 214 outputs a writeenable signal indicating that writing is possible, together with anaddress indicated by the write pointer to the entry RAM 220. On theother hand, as a result of the arbitration, in a case of receiving aspecification of a read address from the read pointer register 213, thebus arbitration unit 214 outputs an address indicated by the readpointer to the entry RAM 220.

The entry data register 215 temporarily stores the entry data read fromthe entry RAM 220, and outputs the stored entry data to the entry datacontrol unit 211.

The status data register 216 temporarily stores request statusinformation read from the request status RAM 230, and outputs the storedrequest status information to the entry data control unit 211.

The bus traffic monitoring unit 217 counts the number of times a busysignal has been outputted, representing the fact that the waveformmemory interface unit 200 as a bus master has obtained an access rightwith regard to the bus 14, and a count value is outputted to the entrydata control unit 211 each one sample cycle. It is to be noted that thecount value of the bus traffic monitoring unit 217 is reset each onesample cycle.

FIG. 6 is a block diagram showing a configuration example of the bustraffic monitoring unit 217.

In FIG. 6, the bus traffic monitoring unit 217 is provided with anincrementer 217 a, a selector 217 b, and a register 217 c.

A busy signal from the memory bus interface unit 240 and an outputsignal (count value) of the register 217 c are inputted to theincrementer 217 a. The incrementer 217 a increments the output signal ofthe register 217 c by 1, in response to a busy signal being inputted,and outputs to the selector 217 b.

An output signal of the incrementer 217 a, a zero signal, and the mastercounter mc are inputted to the selector 217 b. The zero signal is asignal that invariably indicates a zero value. Then, in a case in whichthe value of the master counter mc is zero, the selector 217 b selectsthe zero signal, and in a case in which the value of the master countermc is not zero, selects the output signal of the incrementer 217 a. Thesignal selected by the selector 217 b is outputted to the register 217c.

A system clock is inputted to the register 217 c, and a value indicatedby the output signal of the selector 217 b is held, in synchronizationwith respective clocks rising. The register 217 c outputs an outputsignal (traffic information) indicating the value held to theincrementer 217 a and the entry data control unit 211.

Returning to FIG. 5, on receiving memory request information from theentry data control unit 211, the memory request control unit 218 refersto the number of read words and the address of the memory 12 indicatedin the memory request information, to read the waveform sample data fromthe memory 12. At this time, after obtaining an access right to the bus14 via the memory bus interface unit 240, the memory request controlunit 218 reads the waveform sample data from the memory 12.

Furthermore, on input of a reception completion signal (a signalindicating that reading of data from the memory 12 is completed) fromthe memory bus interface unit 240, the memory request control unit 218notifies the entry data control unit 211 that data reading has beencompleted, and goes into a reception state for reading further data.

The entry RAM 220 is provided as local memory of the musical soundgeneration device 20, and stores entry data inputted from the waveformgeneration unit 100.

FIG. 7 is a schematic diagram showing a format of entry data stored inthe entry RAM 220.

In FIG. 7, the number of storage areas that can handle a case in whichthe channels ch0 to ch127 generate sound simultaneously, that is, 128areas, are formed in the entry RAM 220, and the replay mode value m, thestart flag f representing whether or not sound generation has started,the number of request words RW, channel number ch, and a request addressRA are stored in respective storage areas. It is to be rioted that theaddresses shown in FIG. 7 schematically represent the respective storageareas.

Furthermore, with regard to the respective storage areas, addresses arecyclically specified by a write pointer and a read pointer. That is, theentry RAM 220 forms a ring buffer that sequentially stores plural entrydata.

Returning to FIG. 5, the request status RAM 230 is provided as localmemory of the musical sound generation device 20, and stores requeststatus information representing content of the previous read requestinputted from the entry data control unit 211.

FIG. 8 is a schematic diagram showing a format of request statusinformation stored in the request status RAM 230.

In FIG. 8, in the request status RAM 230, storage areas are formed forrequest status information corresponding to respective entry data of theprevious time for which waveform sample data have already been read fromthe memory 12. A request address RA processed in the previous samplingcycle, and based on the address, the number XW of words already read,and the replay mode value m are stored in the respective storage areas.

Furthermore, with regard to the respective storage areas, addresses arecyclically specified by a write pointer and a read pointer. That is, therequest status RAM 230 forms a ring buffer that sequentially stores aplurality of request status entry data.

It is to be noted that the addresses shown in FIG. 8 schematicallyrepresent the respective storage areas.

Returning to FIG. 5, in a case of a request to read waveform sample datain the memory 12 from the memory request control unit 218, the memorybus interface unit 240 requests an access right with respect to the bus14, and after obtaining the access right, reads the waveform sample datafrom the memory 12. At this time, the memory bus interface unit 240outputs a busy signal indicating that it holds the access right to thebus 14, to the bus traffic monitoring unit 217.

Storage areas corresponding to the respective channels ch0 to ch127 areformed in the sample data buffer RAM 250, and the waveform sample dataread from the memory 12 are stored in the respective storage areas.

FIG. 9 is a schematic diagram showing a format of storage areas in thesample data buffer RAM 250.

In FIG. 9, 128 storage areas corresponding to the channels ch0 to ch127are formed in the sample data buffer RAM 250. Data representing a wavepeak value W is stored in the storage area of each channel, and thenumber (number of words) of sample data stored in one storage area ofthe sample data buffer RAM 250 differs according to the replay modevalue m (according to which of PCM or differential PCM is shown). Here,16 sample data corresponding to a maximum of 16 addresses are stored inone storage area. It is to be noted that the addresses shown in FIG. 9schematically represent respective storage areas.

With respect to the sample data buffer RAM 250, when an address of thesample data buffer RAM 250 is specified by the waveform generation unit100, the waveform sample data stored in the addresses is outputted tothe waveform generation unit 100.

It is to be noted that the sample data buffer RAM 250 is formed by dualport memory, and it is possible to simultaneously perform reading ofdata from the waveform generation unit 100 and writing of data from thememory bus interface unit 240. However, it is also possible for thesample data buffer RAM 250 to be formed by single port memory, byperforming bus arbitration.

Operation

Next, a description is given of operation of the electronic musicalinstrument 1.

Below, operation of the electronic musical instrument 1 is describedusing FIG. 10 to FIG. 12, and FIG. 2 to FIG. 9 are referred to asappropriate.

FIG. 10 is a schematic diagram showing relationships of the mastercounter and time slots of respective channels;

As shown in FIG. 10, in the electronic musical instrument 1, onesampling cycle is defined by a period in which the upper 7 bits of themaster counter mc does one round. Then, in one sample cycle; 128 timeslots are formed corresponding to one count with respect to the upper 7bits of the master counter mc. It is to be noted that the lower 4 bitsof the master counter mc are divided into 16 fields of the respectivetime slots.

In a musical sound generation procedure in the electronic musicalinstrument 1, a process related to generating sound for each channel isdivided into output of an address (entry data) of the memory 12 forreading the waveform sample data, and generation of a digital signalindicating waveform from the waveform sample data.

That is, the electronic musical instrument 1 performs output of entrydata, as a process associated with the time slots of the respectivechannels, and with regard to generation of a digital signal indicatingwaveform and reading of the waveform sample data, selects and executestiming corresponding to an empty state of the bus 14.

FIG. 11 is a schematic diagram showing a generation procedure of amusical sound in the electronic musical instrument 1.

As shown in FIG. 11, in each sampling cycle, when there is a transitionto a time slot corresponding to each channel, the entry data generationunit 113 of the waveform generation unit 100 generates entry data inorder to read musical sound data generated next from the memory 12, inaccordance with the replay mode value m inputted from the mode register102.

For example, after a time slot of channel ch0, the entry data generationunit 113 generates entry data for channel ch0.

It is to be noted that the entry data is generated by the entry datageneration unit 113 only in a case in which sound is being generated forthe channel in question.

The entry data generated by the entry data generation unit 113 is storedin the entry RAM 220 of the waveform memory interface unit 200, inaccordance with the time slot in question, within the time slot inquestion, or accompanying completion of entry data generation after thetime slot ending.

For example, the entry data generated in correspondence with the timeslot of channel ch0 is stored in a storage area of the entry RAM 220indicated by a write pointer, within the time slot of the channel ch0 oraccompanying completion of entry data generation. At this time, inresponse to completion of writing of the entry data, an addressindicated by the write pointer is incremented by 1. Furthermore, theread pointer indicates an address with a storage area smaller by atleast 1 than the write pointer.

In the time slots of the respective channels, this type of entry datageneration and storing in the entry RAM 220 are associated as essentialprocessing.

After the time slot of the channel in question, the entry data controlunit 211 of the waveform memory interface unit 200 determines an emptystate (low traffic state) of the bus 14, based on traffic information ofthe bus 14 inputted from the respective bus traffic monitoring units.For example, if the count value total of busy signals of the bus 14shown in traffic information inputted from the respective bus trafficmonitoring units is less than or equal to a set reference value, thewaveform memory interface unit 200 judges that the occupation rate ofthe bus 14 is low, and starts a process (burst transfer process) to readwaveform sample data of a set data amount from the memory 12.Furthermore, from this state, in a case where the count value hasincreased, the waveform memory interface unit 200 causes a decrease fromthe set data amount and reads from the memory 12, and in a case wherethe count value has decreased, causes an increase from the set dataamount and reads from the memory 12.

A process of reading the waveform sample data can be performed bycollectively reading a plurality of channels; for example, it ispossible to read waveform sample data collectively from the memory 12,in correspondence with entry data of channels ch0 to ch3 during soundgeneration, in response to an empty state of the bus 14.

This type of read waveform sample data is stored in the sample databuffer RAM 250 of the waveform memory interface unit 200, to form acached state.

It is to be noted that the waveform sample data is read from the memory12 after a time slot in which entry data are outputted, and the sampledata buffer RAM 250 forms a cached state at latest until the time slotof the channel in question in the next sampling cycle.

On finishing the abovementioned sampling cycle in which entry data ofthe channels ch0 to ch127 are generated, in the next sampling cycle, thewaveform computation unit 116 sequentially reads the waveform sampledata of the channels ch0 to ch127 from the sample data buffer RAM 250,and outputs the musical sound (that is, a digital signal representing awaveform of the musical sound) to the mixer 21.

By this type of operation, a musical sound is generated after almost onesampling cycle of a time slot in which the entry data has beengenerated. It is to be noted that since the sampling frequency isapproximately 44 kHz, one sampling cycle is approximately 0.02 ms, andthe musical sound is replayed almost without delay.

Specific Operation Example

Next, a description is given concerning a specific example in whichmusical sound is actually generated in the electronic musical instrument1.

FIG. 12 is a schematic diagram showing states in which entry data isstored in the entry RAM 220.

Below, referring to FIG. 12 a description is given concerning an examplein which channel ch3 and channel 10 start generating sound, and then,along with the sound generation of channel 3 being stopped, the soundgeneration of channel 16 starts.

In FIG. 12, in a sampling cycle T1, entry data E031 of channel 3 andentry data E101 of channel 10 in which sound generation has started arestored in address 001 and address 002 of the entry RAM 220.

According to FIG. 12, the entry data E031 is entry data written in thesampling cycle T1, and it is shown that the replay mode has 16 bit PCM,start flag 1 (start of sound generation), number of read words 2,channel 3, and read address “00000000h” (h indicates a hexadecimalrepresentation). Furthermore, the entry data E101 is entry data writtenin the sampling cycle T1, and it is shown that the replay mode has 16bit PCM, start flag 1 (start of sound generation), number of read words2, channel 10, and read address “00000100h”.

It is to be noted that when the sampling cycle T1 finishes, the writepointer (WP in FIG. 12) indicates an address 003, and the read pointer(RP in FIG. 12) indicates an address 001.

Next, in sampling cycle T2, entry data E032 of channel 3 and entry dataE102 of channel 10 in which sound is being generated are stored inaddress 003 and address 004 of the entry RAM 220.

In the entry data E032, there is change with respect to the entry dataE031 to a start flag 0 (not the start of sound generation) and readaddress “00000002h”. Furthermore, in the entry data E102, there is achange with respect to the entry data E101 to a start flag 0 (not thestart of sound generation) and read address “00000102h”.

It is to be noted that when the sampling cycle T2 finishes, the writepointer indicates an address 005, and the read pointer indicates anaddress 003.

Next, in sampling cycle T3, entry data E103 of channel 10 in which soundis being generated and entry data E161 of channel 16 in which soundgeneration has started, are stored in address 005 and address 006 of theentry RAM 220.

In the entry data E103, with respect to the entry data E102 there is achange to read address “00000104h”. Furthermore, the entry data E161 isentry data written in sampling cycle T3, and it is shown that the replaymode has 16 bit PCM, start flag 1 (start of sound generation), number ofread words 2, channel 16, and read, address “00040000h”.

Here, it is understood that since the entry data of channel 3 is notstored in the entry RAM 220, for channel 3 the entry data of thesampling cycle T2 is the last, and sound generation is finished.

It is to be noted that when the sampling cycle T3 is finished, the writepointer indicates address 007 and the read pointer indicate's address005.

Processing Algorithm of Electronic Musical Instrument 1

Next, a description is given concerning a processing algorithm of theelectronic musical instrument 1, implementing the above describedoperations.

The processing algorithm of the electronic musical instrument 1 isconfigured principally by 2 processes: an entry data generation processand a waveform generation process.

Entry Data Generation Processing

FIG. 13 is a flowchart showing entry data generation processing.

The entry data generation processing is executed by the waveformgeneration unit 100 of the musical sound generation device 20, and afterstarting with a power supply of the electronic musical instrument 1being turned ON, the execution is repeated until the power supply isturned OFF.

In FIG. 13, when the entry data generation processing is stared, thewaveform generation unit 100 in step S1 determines the current time slotbased on the master counter mc. Specifically, the waveform generationunit 100 determines which channel the current time slot corresponds to.

In step S2, the waveform generation unit 100 makes a determination as towhether or not there is generated sound of a channel corresponding tothe time slot in question. That is, the waveform generation unit 100determines whether or not a key-pressing action corresponding to thechannel in question is carried out.

In a case in which there is no sound generation for a channelcorresponding to the time slot in question, a determination of NO ismade in step S2, and processing proceeds to step S5.

Against this, in a case in which there is sound generation for a channelcorresponding to the time slot in question, a determination of YES ismade in step S2, and processing proceeds to step S3.

In step S3, the waveform generation unit 100 generates entry data of achannel in which sound is generated.

In step S4, the waveform generation unit 100 stores entry data in theentry RAM 220. At this time, the entry data is written to an address ofthe entry RAM 220 indicated by the write pointer.

In step S5, the waveform generation unit 100 determines, with respect toone sampling cycle, whether or not a time slot of the final channel hasended.

In a case in which, in one sampling cycle, the time slot of the finalchannel has not ended, a determination of NO is made in step S5, andprocessing transitions to step S1.

Against this, in a case in which, in one sampling cycle, the time slotof the final channel has ended, a determination of YES is made in stepS5, and processing transitions to step S6.

In step S6, the waveform generation unit 100, with respect to a channelgenerating sound, prescribes generation of a waveform of one samplecycle to the waveform computation unit 116.

When this type of processing of step S6 ends, the entry data generationprocessing ends.

In FIG. 13, the processing of waveform generation specifying (step S6)is executed after ending of the entry data generation of all channels,but this processing may also be performed at predetermined timing in atime slot interval before this.

Waveform Generation Processing

FIG. 14 is a flowchart showing waveform generation processing.

The waveform generation processing is executed by the waveform memoryinterface unit 200 of the musical sound generation device 20, and afterstarting with the power supply of the electronic musical instrument 1being turned ON, the execution is repeated until the power supply isturned OFF.

In FIG. 14, when the waveform generation processing is started, thewaveform memory interface unit 200 determines an empty state of the bus14, in step S11.

In step S12, the waveform memory interface unit 200 reads entry data ofthe number of channels corresponding to an empty state from the entryRAM 220. At this time, the entry data is read sequentially from anaddress of the entry RAM 220 indicated by the read pointer.

In step S13, the waveform memory interface unit 200 refers to the readentry data and reads waveform sample data from the memory 12.

In step S14, the waveform memory interface unit 200 stores the waveformsample data read from the memory 12 in the sample data buffer RAM 250.

In step S15, the waveform memory interface unit 200 performs adetermination as to whether or not the waveform sample data of allchannels in one sampling cycle have been read from the memory 12.

In a case in which the waveform sample data of all channels in onesampling cycle have not been read from the memory 12, a determination ofNO is made in step S15, and processing proceeds to step S11.

Against this, in a case in which the waveform sample data of allchannels in one sampling cycle have been read from the memory 12, adetermination of YES is made in step S15, and processing proceeds tostep S16.

In step S16, the waveform memory interface unit 200 generates a digitalsignal representing a waveform of a musical sound from the waveformsample data of each channel stored in the sample data buffer RAM 250. Instep S16, the waveform memory interface unit 200 outputs a digitalsignal representing a waveform of a musical sound of each channel.

In this way, musical sounds of respective channels are synthesized bythe mixer 21, and the musical sounds are outputted from a speaker or thelike, via the DAC 22.

In FIG. 14, the musical sound generation processing (step S16) isexecuted after ending the waveform sample data reading of all channels,but the processing may also be performed at predetermined timing withinan earlier time slot interval.

As described above, the electronic musical instrument 1 according to thepresent embodiment stores the waveform sample data in the memory 12 as ashared memory, and generated sound of a plurality of channelscorresponding to a polyphonic number is processed by time division, bythe musical sound generation device 20.

With regard to each channel in which sound is generated, the electronicmusical instrument 1 performs generation of entry data indicating a readaddress of the memory 12, in a time slot of the channel in question, tobe stored in the entry RAM 220.

Thereafter, the electronic musical instrument 1 reads the waveformsample data of a predetermined channel from the memory 12, in responseto an empty state of the bus 14, to e stored in the sample data bufferRAM 250, which is local memory.

When the waveform sample data of all channels in which sound isgenerated is stored in the sample data buffer RAM 250, with respect toone sampling cycle, digital signals of a waveform presenting a musicalsound are generated sequentially, with respect to each channel, andoutputted to the mixer 21.

Therefore, compared to a case, in a time slot of each channel, ofperforming computation of a read address of the memory 12, reading ofthe waveform sample data from the memory 12, and as far as generation ofa digital signal of a waveform representing a musical sound, it ispossible to realize a reduction in processing amount in each time slot.

That is, according to the present invention, it is possible to raise theefficiency of processing for generating musical sound in the musicalsound generation device.

Furthermore, since the waveform sample data is read from the memory 12using time in a period outside of a time slot of each channel, it ispossible to access the memory 12 at more appropriate timing.

Furthermore, when the waveform sample data is read from the memory 12,in order to determine the data amount read at one time, by referring tothe traffic information of the bus 14, it is possible to perform readingof data more rapidly in a permitted range in accordance with an emptystate of the bus 14.

Furthermore, in the electronic musical instrument 1 according to thepresent embodiment, a storage area of the entry RAM 220 is cyclicallyspecified by a write pointer and a read pointer.

Therefore, in the electronic musical instrument 1, with regard tocontinuously reading the waveform sample data in the plurality ofchannels, it is possible to write or read data that are a target ofreading for each channel, in appropriate sequence.

Modified Example

In the first embodiment, a description was given in which, in a case ofreading entry data stored in the entry RAM 220, reading is performed inwriting sequence, and the waveform sample data are read from a readaddress of the memory 12 indicated by the entry data.

Against this, it is possible to refer to the entry data of a pluralityof channels within one sampling cycle, and to change the entry dataprocessing sequence (reading sequence), so as to collectively readcontinuous read addresses of the memory 12.

That is, by referring to read addresses with respect to entry data ofthe plurality of channels stored in the entry RAM 220, and rearrangingthe entry data in a sequence in which address continuity is higher, itis possible to sequentially read the entry data by the read pointer.

In a case of performing this type of processing, since it is possible toincrease the data amount in a burst transfer from the memory 12, theusage efficiency of the bus 14 can be increased, and it is possible toperform processing to generate musical sound more efficiently.

It is to be noted that the present invention is not limited to theembodiment described above, and modifications, improvement and the likethat are within a scope in which an object of the present invention canbe realized, are included in the present invention.

In the embodiment described above, a description was given of an exampleof a case in which the musical sound generation device 20 to which thepresent invention is applied is a sound source of an electronic musicalinstrument, but there is no particular limitation to this.

For example, the present invention can be applied generally to anelectronic device having a sound generation function. Specifically, asexamples the present invention can be applied to notebook personalcomputers, mobile terminals, portable game machines, or the like.

The series of processing described above can be executed by hardware,and can be executed by software.

In other words, configurations in FIGS. 2, 3, and 5 are only examples,and there is no particular limitation. That is, it is sufficient if afunction that can execute the overall series of processing describedabove is provided in the musical sound generation device 20, and thereis no particular limitation to the examples of FIGS. 2, 3, and 5, as tohow functional blocks are used in order to realize the functions.

Furthermore, one functional block may be configured by a hardware unit,or may be configured by a software unit, or may be configured by acombination thereof.

In a case of executing the series of processing by software, a programconfiguring the software is installed from a network or a recordingmedium, to a computer or the like.

The computer may be a computer embedded in dedicated hardware. Or, thecomputer may be a computer in which various types of function areexecuted by installing various types of program, for example, a generalpurpose personal computer.

A recording medium that contains this type of program may be configurednot only by removable media 31 of FIG. 1 distributed separately from adevice main unit in order to provide a program to a user, but may beconfigured by a recording medium provided to the user in a state ofbeing embedded in advance in the device main unit. The removable media31 is configured, for example, by a magnetic disk (including a floppydisk), an optical disk, a magnetic optical disk, or the like. An opticaldisk is configured, for example, by a CD-ROM (Compact Disk-Read OnlyMemory), a DVD (Digital Versatile Disk), or the like. A magnetic opticaldisk is configured by an MD (Mini-Disk) or the like. Furthermore, therecording medium provided to the user in a state of being embedded inadvance in the device main unit is configured, for example, by the ROM12 of FIG. 1 in which a program is recorded, a hard disk contained inthe storage unit 18 of FIG. 1, or the like.

It is to be noted that in the present specification, steps describing aprogram recorded in the recording medium clearly include processingperformed chronologically with a sequence thereof, but need notnecessarily be processing chronologically and can be processing executedin parallel or individually.

Furthermore, in the present specification, system terminology representsgeneral devices configured by a plurality of devices, a plurality ofinstruments, or the like.

A description has been given above concerning several embodiments of thepresent invention, but these embodiments are merely examples and are notintended to limit the technical scope of the present invention. Thepresent invention can have various other embodiments, and in additionvarious types of modification such as abbreviations or substitutions canbe made within a range that does not depart from the scope of theinvention. These embodiments or modifications are included in the rangeand scope described in the present specification and the like, and areincluded in the invention and an equivalent range thereof described inthe scope of the claims.

What is claimed is:
 1. A musical sound generation device comprising: aplurality of sound generation channels that generate musical sound; anaddress calculator that calculates an address in order to read, from awaveform memory connected by a bus, waveform data to be assigned to therespective sound generation channels, by time division, for each of thesound generation channels; an address memory that associates and storesaddresses calculated by the address calculator and the sound generationchannels; a bus traffic detection unit that detects traffic informationof the bus; a waveform data reader that reads an address stored in theaddress memory, when it is determined that the bus is in a low trafficstate based on the traffic information of the bus detected by the bustraffic detection unit, and reads waveform data from the waveform memorybased on said read address; a waveform generation prescription unit thatprescribes assigning waveform data read by the waveform data reader to acorresponding sound generation channel, and generating a musical soundfor the sound generation channel to which said waveform data isassigned; and a read data amount determination unit that determines aread data amount that is to be read from the waveform memory by thewaveform data reader, based on an amount of traffic detected by the bustraffic detection unit.
 2. A musical sound generation device comprising:a plurality of sound generation channels that generate musical sound; anaddress calculator that calculates an address in order to read, from awaveform memory connected by a bus, waveform data to be assigned to therespective sound generation channels, by time division, for each of thesound generation channels; an address memory that associates and storesaddresses calculated by the address calculator and the sound generationchannels; a waveform data reader that reads an address stored in theaddress memory, when it is determined that the bus is in a low trafficstate based on detected traffic information of the bus, and readswaveform data from the waveform memory based on said read address; awaveform generation prescription unit that prescribes assigning waveformdata read by the waveform data reader to a corresponding soundgeneration channel, and generating a musical sound for the soundgeneration channel to which said waveform data is assigned; a writingarea prescription unit that prescribes a storage area of the addressmemory for storing an address calculated by the address calculator; anda reading area prescription unit that prescribes a storage area in whichan address is read in the address memory; wherein the writing areaprescription unit and the reading area prescription unit cyclicallyprescribe a storage area of the address memory.
 3. A non-transitorycomputer-readable storage medium having a program stored thereon whichis executable by a computer to perform functions comprising: calculatingan address in order to read, from a waveform memory connected by a bus,waveform data to be assigned to respective ones of a plurality of soundgeneration channels for generating a musical sound, by time division,for each of the sound generation channels; associating and storing thecalculated addresses and sound generation channels in an address memory;detecting traffic information of the bus; reading an address stored inthe address memory, when it is determined that the bus is in a lowtraffic stated based on the detected traffic information of the bus, andreading waveform data from the waveform memory based on said readaddress; and prescribing assigning the read waveform data to acorresponding sound generation channel, and generating a musical soundfor the sound generation channel to which said waveform data isassigned; wherein a data amount to be read from the waveform memory whenthe waveform data is read is based on an amount of traffic detected whendetecting the traffic information of the bus.
 4. A non-transitorycomputer-readable storage medium having a program stored thereon whichis executable by a computer to perform functions comprising: calculatingan address in order to read, from a waveform memory connected by a bus,waveform data to be assigned to respective ones of a plurality of soundgeneration channels for generating a musical sound, by time division,for each of the sound generation channels; associating and storing thecalculated addresses and sound generation channels in an address memory;reading an address stored in the address memory, when it is determinedthat the bus is in a low traffic stated based on detected trafficinformation of the bus, and reading waveform data from the waveformmemory based on said read address; and prescribing assigning the readwaveform data to a corresponding sound generation channel, andgenerating a musical sound for the sound generation channel to whichsaid waveform data is assigned; wherein the method further comprisescyclically specifying a storage area of the address memory by:prescribing a storage area of the address memory for storing thecalculated address; and prescribing a storage area in which an addressis read in the address memory.
 5. A musical sound generation methodcomprising: calculating an address in order to read, from a waveformmemory connected by a bus, waveform data to be assigned to respectiveones of a plurality of sound generation channels for generating amusical sound, by time division, for each of the sound generationchannels; associating and storing the calculated addresses and soundgeneration channels in an address memory; detecting traffic informationof the bus; reading an address stored in the address memory, when it isdetermined that the bus is in a low traffic state based on the detectedtraffic information of the bus, and reading waveform data from thewaveform memory based on said read address; and prescribing assigningthe read waveform data to the corresponding sound generation channel,and generating a musical sound for a sound generation channel to whichsaid waveform data is assigned; wherein a data amount to be read fromthe waveform memory when the waveform data is read is based on an amountof traffic detected by detecting the traffic information of the bus. 6.A musical sound generation method comprising: calculating an address inorder to read, from a waveform memory connected by a bus, waveform datato be assigned to respective ones of a plurality of sound generationchannels for generating a musical sound, by time division, for each ofthe sound generation channels; associating and storing the calculatedaddresses and sound generation channels in an address memory; reading anaddress stored in the address memory, when it is determined that the busis in a low traffic state based on detected traffic information of thebus, and reading waveform data from the waveform memory based on saidread address; prescribing assigning the read waveform data to thecorresponding sound generation channel, and generating a musical soundfor a sound generation channel to which said waveform data is assigned;and cyclically specifying a storage area of the address memory byprescribing a storage area of the address memory in order to store thecalculated address and prescribing a storage area to read an address inthe address memory.
 7. A musical instrument comprising: a waveformmemory; a musical sound generation device; and a bus connecting thewaveform memory and the musical sound generation device to each other;the musical sound generation device comprising: a plurality of soundgeneration channels that generate musical sound; an address calculatorthat calculates an address in order to read, from the waveform memoryconnected by the bus, waveform data to be assigned to the respectivesound generation channels, by time division, for each of the soundgeneration channels; an address memory that associates and storesaddresses calculated by the address calculator and the sound generationchannels; a bus traffic detection unit that detects traffic informationof the bus; a waveform data reader that reads an address stored in theaddress memory, when it is determined that the bus is in a low trafficstate based on the traffic information of the bus detected by the bustraffic detection unit, and reads waveform data from the waveform memorybased on said read address; a waveform generation prescription unit thatprescribes assigning waveform data read by the waveform data reader to acorresponding sound generation channel, and generating a musical soundfor the sound generation channel to which said waveform data isassigned; and a read data amount determination unit that determines aread data amount that is to be read from the waveform memory by thewaveform data reader, based on an amount of traffic detected by the bustraffic detection unit.
 8. A musical instrument comprising: a waveformmemory; a musical sound generation device; and a bus connecting thewaveform memory and the musical sound generation device to each other;the musical sound generation device comprising: a plurality of soundgeneration channels that generate musical sound; an address calculatorthat calculates an address in order to read, from the waveform memoryconnected by the bus, waveform data to be assigned to the respectivesound generation channels, by time division, for each of the soundgeneration channels; an address memory that associates and storesaddresses calculated by the address calculator and the sound generationchannels; a waveform data reader that reads an address stored in theaddress memory, when it is determined that the bus is in a low trafficstate based on detected traffic information of the bus, and readswaveform data from the waveform memory based on said read address; awaveform generation prescription unit that prescribes assigning waveformdata read by the waveform data reader to a corresponding soundgeneration channel, and generating a musical sound for the soundgeneration channel to which said waveform data is assigned; a writingarea prescription unit that prescribes a storage area of the addressmemory for storing an address calculated by the address calculator; anda reading area prescription unit that prescribes a storage area in whichan address is read in the address memory; wherein the writing areaprescription unit and the reading area prescription unit cyclicallyprescribe a storage area of the address memory.